Azo compound and salt thereof, and dye-containing polarizing film comprising the compound or salt

ABSTRACT

Disclosed is an azo compound represented by the general formula (1) or a salt thereof: 
     
       
         
         
             
             
         
       
         
         
           
             wherein R1 and R2 independently represent a hydrogen atom, a lower alkyl group or a lower alkoxy group; and n represents 1 or 2. Also disclosed are a dye-containing polarizing film and a dye-containing polarizing plate, each of which comprises a polarizing film base material and the azo compound contained in the base material.

TECHNICAL FIELD

The present invention relates to a novel azo compound and a saltthereof, and a dye-containing polarizing film comprising the compound orsalt.

BACKGROUND ART

A polarizing plate having a function to transmit or shield light is afundamental constituent element of a display device such as a liquidcrystal display (LCD) along with liquid crystals which have a functionof switching light. The area of application of this LCD has expandedbroadly from small items such as an electronic calculator, a watch, andthe like in the early day to a notebook computer, a word processor, aliquid crystal projector, a liquid crystal television, a car navigationsystem, indoor and outdoor measurement instruments, and the like. Also,the LCD is used in broad conditions from low to high temperature, fromlow to high humidity, and from low to high light intensity. Thus, apolarizing plate having high polarizing performance and excellentdurability is desired.

At present, a polarizing film is manufactured by dyeing a polarizingfilm substrate with or incorporating therein iodine or a dichromatic dyeas a polarizing element, wherein the substrate is a stretched andoriented film of polyvinyl alcohol or its derivative, or an orientedfilm of polyene prepared by dehydrochlorination of a polyvinyl chloridefilm or dehydration of a polyvinyl alcohol film. Among these, an iodinepolarizing film which uses iodine as the polarizing element exhibitssuperior initial polarizing performance. On the other hand, thispolarizing film is weak to moisture and heat, and when it is used for along time under a condition of high temperature and high humidity, therearises a problem of durability. In order to improve durability, methodssuch as treatment of a polarizing film with formalin or an aqueoussolution containing boric acid, use of a polymer film of low moisturepermeability as a protect film, and the like are considered. However,the effects of these methods are not satisfactory. On the other hand, adye-containing polarizing film comprising a dichromatic dye as apolarizing element has better humidity resistance and heat resistancethan an iodine polarizing film, but, generally, initial polarizingperformance of the dye-containing polarizing element is insufficient.

In a neutral color polarizing film produced by adsorbing severaldichromatic dyes to a polymer film followed by orientation, if there islight leakage (color leakage) of a specific wavelength in the wavelengthrange of visible light, in a state (the perpendicular position) that twopolarizing films are superimposed on each other in such a way that theirorientation directions are perpendicular to each other, the hues of theliquid crystal display may change in the dark state when the polarizingfilms are fitted to the liquid crystal display panel. Thus, in order toprevent the color change of a liquid crystal display due to colorleakage of a specific wavelength in the dark state when a polarizingfilm is fitted to a liquid crystal display device, it is necessary touniformly lower the average light transmittance at the perpendicularposition (perpendicular average light transmittance) in the wavelengthrange of visible light.

Further, in a case of a color liquid crystal projection display, namely,a color liquid crystal projector, a polarizing plate is used for aliquid crystal image-forming part. In this application, the iodinepolarizing plate was used formerly, which has good polarizationperformance and exhibits neutral gray color. However, as mentionedabove, the iodine polarizing plate has a problem that its lightresistance, heat resistance, and wet heat resistance are insufficient,because iodine is a polarizer. In order to solve this problem, a neutralgray polarizing plate using a dye-containing dichromatic colorant as apolarizer has come to be used. In a neutral gray polarizing plate,colorants of three primary colors are generally used in combination inorder to improve transmittance in the entire wavelength range of visiblelight and polarization performance averagely. Thus, there is a problemthat to the demand of the marketplace for more brightness as in thecolor liquid crystal projector, the transmittance is still poor, and inorder to realize brightness, it is necessary to increase intensity ofthe light source. In order to solve this problem, three polarizingplates corresponding to three primary colors, namely, plates for each ofthe blue channel, the green channel, and the red channel have come to beused.

Decrease in brightness cannot be avoided because an image of such asmall area as 0.5 to 3 inches is magnified to about several tens to onehundred and tens of inches, and light is absorbed considerably by thepolarizing plate. Therefore, as the light source, one of high luminanceis used. Furthermore, desire for further increase in brightness of aliquid crystal projector is strong and, as a result, the intensity ofthe light source used is inevitably growing stronger. Along with this,the amounts of light and heat which the polarizing film receives areincreasing.

However, conventional polarizing plates have not yet satisfied themarket needs sufficiently in terms of polarization characteristics, therange of absorption wavelength, hues, and the like. Furthermore, amongthe polarizing plates corresponding to three primary colors for a colorliquid crystal projector, namely, the plates for each of the bluechannel, the green channel, and the red channel, none is good in allaspects of brightness, polarization performance, durability under acondition of high temperature and high humidity, and resistance toprolonged irradiation of light. Improvement is thus desired.

As a dye having absorption characteristics especially for the bluechannel (400 to 500 nm), there are used C.I. Direct Yellow 12, C.I.Direct Yellow 28, C.I. Direct Yellow 44, C.I. Direct Orange 39, C.I.Direct Orange 72, C.I. Direct Orange 26, and dyes described in PatentDocuments 1 to 3, and the like. However, polarization characteristics ofthe polarizing film using these dyes are poor, causing problems that,when displaying white images, yellowish images are provided and thecolor temperatures do not rise.

Patent Document 1: JP-A-2001-108828

Patent Document 2: JP-A-2001-240762

Patent Document 3: JP-A-2003-215338

Patent Document 4: JP-A-60-168743

Patent Document 5: JP-A-2003-35819

Patent Document 6: JP-A-2001-33627

Patent Document 7: Japanese Patent No. 2622748

Patent Document 8: JP-A-60-156759

Non-patent Document 1: “Senryo Kagaku (Dye Chemistry)” by Yutaka Hosoda(Published by Gihodo Co., Ltd., Japan) p. 626

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a polarizing plate ofhigh performance having excellent polarization performance andresistance to humidity, heat, and light. Further, another object of thepresent invention is to provide a polarizing plate of high performancewhich does not cause color leakage at the perpendicular position in thewavelength range of visible light and which has excellent polarizationperformance and resistance to humidity, heat, and light, the polarizingplate being a neutral color polarizing plate produced by adsorbing twoor more dichromatic dyes in a polymer film, followed by orientationthereof.

A further object of the present invention is to provide color polarizingplates of high performance corresponding to three primary colors for acolor liquid crystal projector, which are good in all of brightness,polarization performance, durability, and light resistance.

The present inventors conducted diligent research in order to accomplishthese objects and, as a result, found that a polarizing film and apolarizing plate comprising a novel azo compound and/or a salt thereofshow excellent polarizing performance and resistance to humidity, heat,and light. This finding led to the present invention. Namely, thepresent invention includes the following embodiments:

(1) An azo compound represented by the following formula (1) and a saltthereof:

wherein R1 and R2 each independently represent a hydrogen atom, a loweralkyl group, and a lower alkoxy group; n is 1 or 2.(2) The azo compound and a salt thereof according to (1), wherein R1 andR2 are each independently one of a hydrogen atom, a methyl group, and amethoxy group.(3) The azo compound and a salt thereof according to (1), wherein R1 andR2 are a hydrogen atom.(4) A dye-containing polarizing film comprising at least one azocompound and/or salt thereof according to any one of (1) to (3),contained in a polarizing film substrate.(5) A dye-containing polarizing film comprising at least one azocompound and/or salt thereof according to any one of (1) to (3), and atleast one other organic dye, contained in a polarizing film substrate.(6) A dye-containing polarizing film comprising two or more azocompounds and/or salts thereof according to any of (1) to (3), and atleast one other organic dye, contained in a polarizing film substrate.(7) The dye-containing polarizing film according to any one of (4) to(6), wherein the polarizing film substrate is a film comprising apolyvinyl alcohol resin(8) A dye-containing polarizing plate comprising a transparentprotective layer adhered on at least one surface of a dye-containingpolarizing film according to any one of (4) to (7).(9) A color polarizing plate for a liquid crystal projector, wherein adye-containing polarizing film or a dye-containing polarizing plateaccording to any one of (4) to (8) is used.

The azo compound and salt thereof of the present invention are useful asa dye for a polarizing film. The polarizing film containing thesecompounds has a high polarizing performance comparable to a polarizingfilm using iodine and also has excellent durability. Thus, the formerpolarizing film is suitable for various liquid crystal displays andliquid crystal projectors, in-vehicle applications which require highpolarizing performance and durability, and for applications inindustrial instrument displays used in various environments.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention relates to an azo compound represented by theformula (1) in the form of a free acid and a salt thereof. In theformula (1), R1 and R2 are each independently a hydrogen atom, a loweralkyl group, and a lower alkoxy group; preferably R1 and R2 are ahydrogen atom and a lower alkyl group; especially preferably R1 is ahydrogen atom or a methyl group and R2 is a hydrogen atom; and nrepresents 1 or 2. In the present invention, a lower alkyl group and alower alkoxy group refer to an alkyl group and an alkoxy group, bothhaving 1 to 4 carbon atoms. Next, specific examples of azo compoundsrepresented by the formula (1), which are used in the present invention,are shown below (formulae (2) to (6)). In the following formulae, thesulfonic acid group, carboxylic group, and hydroxyl group are shown infree acid forms.

The azo compound represented by the formula (1) in the form of a freeacid can easily be manufactured by carrying out publicly knowndiazotization and coupling reactions according to a generalmanufacturing method of azo dyes such as described in Non-PatentDocument 1. As a specific method of manufacture, 4-aminobenzoic acid isdiazotized and coupled with an aniline represented by the followingformula (A) to obtain a monoazoamino compound (the following formula(B)).

wherein R1 and R2 represent the same meaning as in the formula (1).

Then, this monoazoamino compound is reacted with4,4′-dinitrostilbene-2,2′-sulfonic acid under an alkaline condition,followed by reduction with glucose to obtain the azo compoundrepresented by the formula (1).

In the above reaction, the diazotization step may be carried outaccording to a usual method of mixing a nitrite salt such as sodiumnitrite into a solution or a suspension of a diazo component in anaqueous mineral acid such as aqueous hydrochloric acid or aqueoussulfuric acid, or it may be carried out according to a reverse methodwhere a nitrite salt is added beforehand to a neutral or weakly alkalineaqueous solution of the diazo component and this solution is mixed withthe mineral acid. The temperature of diazotization is suitably −10 to+40° C. Further, the coupling step with an aniline is carried out bymixing an acidic aqueous solution of the latter in aqueous hydrochloricacid, aqueous acetic acid, or the like with the respectiveabovementioned diazo solutions and reacting at a temperature of −10 to+40° C. under an acidic condition of pH 2 to 7.

In a reaction of the monoazoamino compound with4,4′-dinitrostilbene-2,2′-sulfonic acid, the condensation step under analkaline condition is carried out under a strongly alkaline condition byuse of sodium hydroxide, lithium hydroxide, and the like. Theconcentration of the alkali is suitably 2% to 10% and the temperature issuitably 70 to 100° C. The number for n in the formula (1) can beadjusted by changing the charging ratio of the monoazoamino compound and4,4′-dinitrostilbene-2,2′-sulfonic acid. In the glucose reduction step,it is common to use 0.5 to 1.2 equivalents of glucose under an alkalinecondition.

Further, in the present invention, the azo compound represented by theformula (1) may be used as a free acid and, as a salt as well. The saltincludes alkali metal salts such as a lithium salt, a sodium salt, apotassium salt, and the like; an ammonium salt; and organic salts suchas an amine salt. Generally, a sodium salt is used.

In the synthesis of an azo compound represented by the formula (1), thesubstituent of the primary coupling component, anilines which may havesubstituents (R1, R2), includes a methyl group, an ethyl group, amethoxy group, and an ethoxy group. Any one or two of these substituentsmay be attached. The position of their attachment is, relative to theamino group, position 2, position 3, positions 2 and 5, positions 3 and5, or positions 2 and 6. Among these, attachment to position 3 andpositions 2 and 5 is preferable. Examples of the anilines include, forexample, aniline, 2-methylaniline, 3-methylaniline, 2-ethylaniline,3-ethylaniline, 2,5-dimethylaniline, 2,5-diethylaniline,2-methoxyaniline, 3-methoxyaniline, 2-methoxy-5-methylaniline,2,5-dimethoxyaniline, 3,5-dimethylaniline, 2,6-dimethylaniline, and3,5-dimethoxyaniline. The amino group of these anilines may beprotected. As the protecting group, there may be mentioned aω-methanesulfonic acid group.

Further, in the polarizing film or polarizing plate of the presentinvention, the azo compound represented by the formula (1) or a saltthereof may be used singly or in combination of several kinds. Also, asrequired, one or more other organic dyes may be used together. There isno particular restriction on dyes which are used together, but they arepreferably dyes having absorption characteristics in a wavelength rangedifferent from those of the azo compounds or salts thereof according tothe present invention and having high dichroism. Examples include C.I.Direct Red 2, C.I. Direct Red 31, C.I. Direct Red 79, C.I. Direct Red81, C.I. Direct Red 247, C.I. Direct Green 80, C.I. Direct Green 59, andthe dyes described in Patent Document Nos. 5 to 8. These dyes may beused as free acids, alkali metal salts (for example, Na salt, K salt, Lisalt), ammonium salts, or amine salts.

When other organic dyes are used together as required, the kind oforganic dye incorporated varies depending on whether the intendedpolarizing film is a neutral polarizing film, a color polarizing filmfor a liquid crystal projector, or other color polarizing film. Theproportion of one or more kinds of the above organic dyes incorporatedcollectively is not particularly limited, but is generally preferably inthe range of 0.1 to 10 parts by weight based on the weight of the azocompound of the formula (1) or a salt thereof.

The polarizing films having various hues and neutral color used for thepolarizing plates of the present invention or the polarizing plates fora liquid crystal projector can be prepared by incorporating the azocompounds represented by the formula (1) or salts thereof together withother organic dyes as necessary into a polymer film, a material for thepolarizing film, by a publicly known method. To the polarizing filmobtained is attached a protecting film to produce a polarizing plate,and then, as required, a protecting layer or an AR (anti-reflection)layer, a support, and the like are disposed thereon, to be used for aliquid crystal projector, an electronic calculator, a watch, a notebookcomputer, a word processor, a liquid crystal television, a carnavigation system, indoor and outdoor measuring instruments, a display,and the like.

As the substrate (polymer film) used for the polarizing film of thepresent invention, polyvinyl alcohol substrates are preferable. As thepolyvinyl alcohol substrates, there may be cited, for example, polyvinylalcohol or a derivative thereof, and those obtained by modifying eitherof these with an olefin such as ethylene or propylene; an unsaturatedcarboxylic acid such as crotonic acid, acrylic acid, methacrylic acid,or maleic acid; and the like. Among these, a film comprising polyvinylalcohol or a derivative thereof is preferably used in terms of anadsorption property towards dyes and an orientation property. Thethickness of the substrate is usually 30 to 100 μm, preferably about 60to 90 μm.

In incorporating the azo compound of the formula (1) or a salt thereofinto such a polymer film, a method of dyeing the polymer film is usuallyadopted. Dyeing, for example, is carried out as follows. First, the azocompound and/or a salt thereof according to the present invention andother dyes, as required, are dissolved in water to prepare a dye bath.The concentration of dyes in the dye bath is not particularly limitedbut usually selected from the range of about 0.001 to 10% by weight.Furthermore, a dyeing auxiliary may be used as required and, forexample, sodium sulfate is suitably used in a concentration of about 0.1to 10% by weight. Dyeing is carried out by dipping the polymer film inthe dye bath thus prepared for 1 to 10 minutes. The dyeing temperatureis preferably about 40 to 80° C.

Orientation of the water-soluble dye is carried out by stretching thepolymer film dyed as described above. As a stretching method, anypublicly known method such as a wet method, dry method, and the like maybe employed. In some cases, stretching of the polymer film may be donebefore dyeing. In this case, orientation of the water-soluble dye isperformed at the time of dyeing. The polymer film in which thewater-soluble dye is incorporated and oriented may, as required, besubjected to an after-treatment such as a boric acid treatment by apublicly known method. Such an after-treatment is carried out in orderto improve light transmittance and degree of polarization of thepolarizing film. The condition of the boric acid treatment variesdepending on the kind of polymer film used and the kind of dye used. Ingeneral, the concentration of boric acid in its aqueous solution is inthe range of 0.1 to 15% by weight, preferably 1 to 10% by weight, andthe treatment is carried out by dipping at the temperature range of 30to 80° C., preferably 40 to 75° C., for 0.5 to 10 minutes. Further, thepolymer film may, as required, be subjected to a fixing treatment at thesame time with an aqueous solution containing a cationic polymercompound.

To one or both surfaces of the dye-containing polarizing film of thepresent invention thus obtained, transparent protective films excellentin optical transparency and mechanical strength may be adhered toproduce a dye-containing polarizing plate. As a material to form theprotective film, there may be used, for example, a cellulose acetatefilm, an acrylic film, a fluorinated film such astetrafluoroethylene/hexafluoropropylene copolymer, and a film composedof a polyester resin, a polyolefin resin, or a polyamide resin.Preferably, a triacetyl cellulose (TAC) film or a cycloolefin film maybe used. The thickness of the protective film is usually 40 to 200 μm.

An adhesive which may be used to adhere the polarizing film and theprotective film together includes a polyvinyl alcohol (PVA) adhesive, anurethane emulsion adhesive, an acrylic adhesive, a polyester-isocyanateadhesive, and the like. Of these, the polyvinyl alcohol adhesive issuitable.

Furthermore, a transparent protective layer may be provided on thesurface of the dye-containing polarizing plate of the present invention.As the protective layer, there may be cited, for example, an acrylic orpolysiloxane hard coat layer and a urethane protective layer. Further,in order to improve the single plate light transmittance further, it ispreferable to provide an AR layer on this protective layer. The AR layermay be formed, for example, by a vapor deposition or sputteringtreatment of a substance such as silicon dioxide or titanium dioxide.The AR layer may also be formed by thinly coating a fluorinatedsubstance. In addition, the dye-containing polarizing plate of thepresent invention may also be used as an elliptically polarizing platein which a phase difference plate is adhered.

The dye-containing polarizing plate of the present invention thusconstituted has a neutral color, causes no color leakage at theperpendicular position in the wavelength range of visible light, andshows excellent polarization performance. Further, it hascharacteristics that even under conditions of high temperature and highhumidity, it shows no discoloration, no deterioration of polarizationperformance, and little light leakage at perpendicular position in therange of visible light.

In the present invention, the color polarizing plate for a liquidcrystal projector includes, as a dichromatic molecule, the azo compoundrepresented by the formula (1) and/or a salt thereof and further, asrequired, other organic dyes mentioned above. Also, the polarizing filmused for a color polarizing plate for a liquid crystal projector isproduced by the same method as that for the aforementioneddye-containing polarizing film. A protective film is further attached tothe polarizing film to produce a dye-containing polarizing plate, whichis, as required, provided with a protective layer, an AR layer, asupport, and the like, and is used as a color polarizing plate for aliquid crystal projector.

As a color polarizing plate for a liquid crystal projector, preferably,the single plate average light transmittance is 39% or higher and theaverage light transmittance at perpendicular position is 0.4% or less inthe wavelength range necessary for the polarizing plate (A. When anultra-high pressure mercury lamp is used: 420 to 500 nm for the bluechannel, 500 to 580 nm for the green channel, and 600 to 680 nm for thered channel; B. Peak wavelength when three primary color LED lamps areused: 430 to 450 nm for the blue channel, 520 to 535 nm for the greenchannel, 620 to 635 nm for the red channel). More preferably, in thewavelength range necessary for the polarizing plate, the single plateaverage light transmittance is 41% or higher and the average lighttransmittance at the perpendicular position is 0.3% or less, morepreferably 0.2% or less. Still more preferably, in the wavelength rangenecessary for the polarizing plate, the single plate average lighttransmittance is 42% or higher and the average light transmittance atthe perpendicular position is 0.1% or less. As mentioned above, thecolor polarizing plate for a liquid crystal projector of the presentinvention has brightness and excellent polarization performance.

The color polarizing plate for a liquid crystal projector of the presentinvention is preferably a polarizing plate with an AR layer which isobtained by providing the above-mentioned AR layer on a polarizing plateconsisting of a polarizing film and a protective film. Further, apolarizing plate with an AR layer and a support is more preferable,which is obtained by adhering the polarizing plate with an AR layer to asupport such as a transparent glass plate.

In addition, the single plate average light transmittance is an averagevalue of light transmittance in a specific wavelength range when naturallight enters one polarizing plate without an AR layer and a support suchas a transparent glass plate provided (hereafter simply referred to as“polarizing plate” in the same sense). The average light transmittanceat the perpendicular position is an average value of light transmittancein a specific wavelength range when natural light enters two polarizingplates, which are superimposed with the orientation directionsperpendicular to each other.

The color polarizing plate for a liquid crystal projector of the presentinvention is used generally as a polarizing plate with a support. Thesupport preferably has a planar section because a polarizing plate isadhered thereto. Also, the support is preferably a molded article ofglass because the polarizing plate is put to an optical use. As a moldedarticle of glass, there may be cited, for example, a glass plate, alens, a prism (for example, a triangle prism or a cubic prism). A lensto which is adhered the polarizing plate may be used as a condenser lenswith a polarizing plate in a liquid crystal projector. Also, a prism towhich is adhered the polarizing plate may be used as a polarizing beamsplitter with a polarizing plate or a dichromatic prism with apolarizing plate in a liquid crystal projector. Further, the polarizingplate may be adhered to a liquid crystal cell. As the glass material,there may be mentioned inorganic glass such as soda glass, borosilicateglass, and sapphire glass; organic glass such as acrylic andpolycarbonate; and the like. Preferable is inorganic glass. Thethickness and size of a glass plate may be chosen as desired. Also, inorder to further improve the single plate light transmittance of thepolarizing plate with a glass, it is preferable to provide an AR layeron one or both sides of the glass surface or polarizing plate surface.

In order to produce a polarizing plate with a support for a liquidcrystal projector, for example, a transparent adhesive(pressure-sensitive adhesive) is coated on the planar section of thesupport and then the polarizing plate of the present invention isattached to this coated surface. Also, a transparent adhesive(pressure-sensitive adhesive) may be coated on the polarizing plate andthen a support may be attached to this coated surface. As the adhesive(pressure-sensitive adhesive) used herein, for example, an acrylic esteradhesive is preferable. In addition, when this polarizing plate is usedas an elliptically polarizing plate, usually a phase difference plateside is adhered to the support, but the polarizing plate side may beadhered to the molded article of glass.

In a color liquid crystal projector using the polarizing plate of thepresent invention, the polarizing plate of the present invention isdisposed on either one or both of the incident side and outgoing side ofa liquid crystal cell. The polarizing plate may or may not be in contactwith the liquid crystal cell, but, in terms of durability, it ispreferable that the plate is not in contact with the liquid crystalcell. When the polarizing plate is in contact with the liquid crystalcell at the outgoing side, there may be used a polarizing plate of thepresent invention having the liquid crystal cell as a support. When thepolarizing plate is not in contact with the liquid crystal cell, theremay preferably be used a polarizing plate of the present invention usinga support other than the liquid crystal cell. Furthermore, in terms ofdurability, the polarizing plates of the present invention arepreferably disposed on both the incident side and outgoing side of theliquid crystal cell. Further, it is preferable that the polarizing platesurface of the polarizing plate of the present invention is disposed onthe liquid crystal cell side, with the support surface thereof on thelight source side. In addition, the incident side of the liquid crystalcell means the light source side, and the opposite side is referred toas the outgoing side.

In a color liquid crystal projector using the polarizing plate of thepresent invention, an ultraviolet light-cutting filter is preferablydisposed between the light source and the polarizing plate with asupport on the incident side. Further, the liquid crystal cell used ispreferably, for example, an active matrix type, which is formed byencapsulating liquid crystals between a transparent substrate on whichan electrode and a TFT (thin film transistor) are formed and, anothertransparent substrate on which the counter electrode is formed. Lightemitted from a light source such as an ultra-high pressure mercury lamp(UHP lamp), a metal halide lamp, a white LED, and the like passesthrough the ultraviolet light-cutting filter, and separates into threeprimary colors, which then passes through the respective colorpolarizing plates with supports for each of blue, green, and redchannels. The light is then integrated, magnified by a projector lens,and projected onto a screen. Alternatively, using LEDs corresponding toeach of blue, green, and red colors, light emitted from LED of eachcolor passes through respective color polarizing plates with supportsfor each of blue, green, and red channels, then is integrated, magnifiedby a projector lens, and projected onto a screen.

The polarizing plate for a color liquid crystal projector thusconstituted has characteristics that its polarization performance isexcellent, and, furthermore, discoloration and deterioration ofpolarization performance do not occur even under a high temperature andhigh humidity condition.

EXAMPLES

Hereinafter the present invention will be described in more detail interms of Examples. However, examples are for illustrative purposes onlyand not meant to limit the scope of the present invention in any manner.In Examples, % and parts are based on weight, unless otherwise noted.

Example 1

13.7 parts of 4-aminobenzoic acid was added to 500 parts of water anddissolved with sodium hydroxide. After cooling, 32 parts of 35% aqueoushydrochloric acid and subsequently 6.9 parts of sodium nitrite wereadded at a temperature of 10° C. or below, and the reaction mixture wasstirred at 5 to 10° C. for 1 hour. To this was added 20.9 parts ofsodium aniline-ω-methanesulfonate and, while the reaction mixture wasstirred at 20 to 30° C., sodium carbonate was added to adjust the pH to3.5. By further stirring, the coupling reaction was completed and amonoazo compound was obtained by filtration. The monoazo compoundobtained was stirred at 90° C. in the presence of sodium hydroxide toobtain 17 parts of a monoazo compound represented by the followingformula (7).

After 12 parts of the monoazo compound represented by the formula (7)and 21 parts of 4,4′-dinitrostilbene-2,2′-sulfonic acid were dissolvedin 300 parts of water, 12 parts of sodium hydroxide was added and thereaction mixture was subjected to condensation reaction at 90° C. Then,the reaction mixture was reduced by 9 parts of glucose, salted out withsodium chloride, and filtered to obtain 16 parts of the azo compoundrepresented by the formula (2). This compound was orange in color andits solution in 20% aqueous pyridine showed an absorption maximum at awavelength of 444 nm.

Example 2

After 12 parts of the monoazo compound represented by the formula (7)and 10 parts of 4,4′-dinitrostilbene-2,2′-sulfonic acid were dissolvedin 300 parts of water, 24 parts of sodium hydroxide was added and thereaction mixture was subjected to condensation reaction at 90° C. Then,the reaction mixture was reduced by 18 parts of glucose, salted out withsodium chloride, and filtered to obtain 20 parts of the azo compoundrepresented by the formula (3). This compound was orange in color andits solution in 20% aqueous pyridine showed an absorption maximum at awavelength of 428 nm.

Example 3

To 500 parts of water was added 13.7 parts of 4-aminobenzoic acid andwas dissolved with sodium hydroxide. After cooling, 32 parts of 35%aqueous hydrochloric acid and, subsequently, 6.9 parts of sodium nitritewere added at a temperature of 10° C. or below and the reaction mixturewas stirred at 5 to 10° C. for 1 hour. To this was added 13.7 parts of2-methoxy-5-methylaniline and, while the reaction mixture was stirred at20 to 30° C., sodium carbonate was added to adjust the pH to 3.5. Byfurther stirring, the coupling reaction was completed and the reactionmixture was filtered to obtain a monoazo compound. The monoazo compoundobtained was stirred at 90° C. in the presence of sodium hydroxide toobtain 26 parts of monoazo compound represented by the following formula(8).

In 300 parts of water, 14 parts of the monoazo compound represented bythe formula (8) and 21 parts of 4,4′-dinitrostilbene-2,2′-sulfonic acidwere dissolved and, after addition of 12 parts of sodium hydroxide, werecondensation reacted at 90° C. Then, the reaction mixture was reduced by9 parts of glucose, salted out with sodium chloride, and filtered toobtain 16 parts of the azo compound represented by the formula (6). Thiscompound was red in color and its solution in 20% aqueous pyridineshowed an absorption maximum at a wavelength of 444 nm.

Example 4

In an aqueous solution kept at 45° C. containing a dye of the compound(2) obtained in Example 1 in a concentration of 0.01% and sodium sulfatein a concentration of 0.1%, a polyvinyl alcohol film of 75 μm inthickness was dipped for 4 minutes. This film was stretched 5-folds at50° C. in a 3% aqueous boric acid solution, washed with water in thestretched state, and dried to obtain a polarizing film.

In Table 1 are shown the (a) maximum absorption wavelength, (b) singleplate transmittance, (c) polarization coefficient, and (d) contrastratio, (b) to (d) being measured at the maximum absorption wavelength ofthe polarizing film obtained.

The transmittance (completely polarized light transmittance (parallel:Ky, perpendicular: Kz)) of polarized light which was radiated indirections parallel and perpendicular to the direction of orientation ofthe polarizing film obtained in the foregoing was measured by aspectrophotometer (U-4100, manufactured by Hitachi, Ltd.).

The polarization coefficient, single plate transmittance of naturallight, transmittance at the perpendicular position when two polarizingplates are superimposed with the directions of orientation perpendicularto each other, and contrast ratio were calculated according to thefollowing equations (1) to (4) from the values of Ky and Kz, obtained bythe aforementioned measurements.(Polarization coefficient)=(Ky−Kz)/(Ky+Kz)  (1)(Single plate transmittance)=(Ky+Kz)/2  (2)(Transmittance at perpendicular position)=Ky×Kz/100  (3)(Contrast ratio)=Ky/Kz  (4)

Example 5

Using an aqueous solution kept at 45° C. containing a dye of thecompound (3) obtained in Example 2 in a concentration of 0.03% andsodium sulfate in a concentration of 0.01%, a polarizing film wasprepared in the same manner as in Example 4. In Table 1 are shown its(a) maximum absorption wavelength, (b) single plate transmittance, (c)polarization coefficient, and (d) contrast ratio, (b) to (d) beingmeasured at the maximum absorption wavelength.

Comparative Example 1

Except that 0.01% aqueous solution of C.I. Direct Orange 39 (a dyecomprising, as a major component, the compound represented by thefollowing structural formula (9)), was used instead of the compound (2)obtained in Example 1, a polarizing film was prepared in the same manneras in Example 4. Its (a) maximum absorption wavelength, (b) single platetransmittance, (c) polarization coefficient, and (d) contrast ratio, (b)to (d) being measured at the maximum absorption wavelength, are shown inTable 1, which shows that the polarization coefficient and contrastratio at the same transmittance were greatly inferior to Examples 4 and5.

TABLE 1 Maximum Polar- Con- Com- absorption Single plate ization trastpound wavelength transmittance coefficient ratio Example 4 (2) 462 nm43.79% 99.55% 443 Example 5 (3) 445 nm 43.82% 99.43% 350 Comparative (9)447 nm 43.79% 99.24% 262 Example 1

Example 6

In an aqueous solution kept at 45° C. containing a dye of the compound(2) obtained in Example 1 in a concentration of 0.01%, C.I. Direct Red81 in a concentration of 0.01%, a dye represented by the followingstructural formula (10) described in Example 1 of Patent Document 7 in aconcentration of 0.03%, a dye represented by the following structuralformula (11) disclosed in Example 23 of Patent Document 8 in aconcentration of 0.03%, and sodium sulfate in a concentration of 0.1%, apolyvinyl alcohol film of 75 ƒm in thickness dipped for 4 minutes. Thisfilm was stretched 5-folds at 50° C. in a 3% aqueous boric acidsolution, washed with water in the stretched state, and dried to obtaina polarizing film of neutral color (gray in the parallel position, blackin the perpendicular position). The single plate average lighttransmittance, polarization coefficient, and contrast ratio of thepolarizing plate, obtained over an entire range of visible light, are asshown in Table 2 and had a high polarization coefficient.

Further, TAC films (80 μm in film thickness, trade name TD-80U, producedby Fujifilm Corporation) were adhered on both surfaces of the polarizingfilm using a PVA adhesive to obtain a polarizing plate of the presentinvention. On one side of this polarizing plate, an acrylic esterpressure sensitive adhesive was applied to afford an adhesive-backedpolarizing plate. This was cut in a size of 30 mm×40 mm and was adheredonto a glass plate of the same size. When this polarizing plates werestored at a high temperature conditions of 105° C. for 1200 hours and ata high temperature and high humidity conditions of 85° C.×85% RH for1200 hours, the changes in polarization coefficients were less than0.1%, showing a long-time durability of the polarizing plates even undera high temperature and high humidity conditions.

Comparative Example 2

Except that a 0.01% aqueous solution of C.I. Direct Orange 39 was usedinstead of the compound (2) obtained in Example 1, a neutral colorpolarizing film was prepared in the same manner as in Example 6. Thesingle plate average light transmittance, polarization coefficient andcontrast ratio over an entire range of visible light are shown in Table2. Compared to the polarizing film of Example 6, not only the singleplate average light transmittance was low, but also polarizingcharacteristics and contrast ratio were greatly inferior.

TABLE 2 Single plate average Polarization Contrast light transmittancecoefficient ratio Example 6 43.99% 99.61% 511 Comparative 43.82% 99.28%277 Example 2

Example 7

In an aqueous solution kept at 45° C. containing a dye of the compound(2) obtained in Example 1 in a concentration of 0.05%, C.I. DirectYellow 28 in a concentration of 0.01%, a dye represented by thefollowing structural formula (12) described as compound No. 1 in PatentDocument 3 in a concentration of 0.01%, and sodium sulfate in aconcentration of 0.1%, a polyvinyl alcohol film of 75 μm in thicknesswas dipped for 4 minutes. This film was stretched 5-folds at 50° C. in a3% aqueous boric acid solution, washed with water in the stretchedstate, and dried to obtain a polarizing film. The maximum absorptionwavelength (λmax) of the polarizing film obtained was 450 nm, and in therange of 430 to 500 nm, the single plate average light transmittance,average light transmittance at perpendicular position and contrast ratioare as shown in Table 3 and had a high polarization coefficient.Further, a TAC film (80 μm in film thickness, trade name TD-80U,produced by Fujifilm Corporation) was adhered on one side of thepolarizing film and on the other side of the polarizing film, a TACfilm, on one side of which had been formed a UV (ultraviolet light)curable hard coat layer in about 10 μm thickness, was adhered using aPVA adhesive to obtain a polarizing plate of the present invention. Onone side of this polarizing plate, an acrylic ester pressure sensitiveadhesive was applied to afford a polarizing plate with a pressuresensitive adhesive layer. Further, on the outer surface of the hard coatlayer, AR (anti-reflection) multi-coating treatment was conducted byvacuum deposition. This was cut in a size of 30 mm×40 mm and was adheredonto a transparent glass plate of the same size with an AR layer on oneside to obtain a color polarizing plate with an AR support for a liquidcrystal projector (for the blue channel) of the present invention. Thecolor polarizing plate for a liquid crystal projector of the presentExample had a high polarization coefficient and, moreover, showed a longlasting durability even at conditions of high temperature and highhumidity. Also, resistance to prolonged irradiation of light wasexcellent.

Example 8

Except that an aqueous solution kept at 45° C. containing a dye of thecompound (3) obtained in Example 2 in a concentration of 0.05%, C.I.Direct Yellow 28 in a concentration of 0.01%, a dye represented by thestructural formula (12) described as compound No. 1 in Patent Document 3in a concentration of 0.01%, and sodium sulfate in a concentration of0.1% was used, a polarizing plate was prepared in the same manner as inExample 7. The single plate average light transmittance, average lighttransmittance at the perpendicular position, and contrast ratio of thepolarizing plate in the range of 430 to 500 nm are shown in Table 3,which had a high polarization coefficient.

Comparative Example 3

Except that an aqueous solution kept at 45° C. containing C.I. DirectOrange 39 in a concentration of 0.05%, C.I. Direct Yellow 28 in aconcentration of 0.01%, a dye represented by the aforementionedstructural formula (12) described as compound No. 1 in Patent Document 3in a concentration of 0.02%, and sodium sulfate in a concentration of0.1% was used, a polarizing plate was prepared in the same manner as inExample 7. This polarizing plate showed the single plate average lighttransmittance, average light transmittance at perpendicular position,and contrast ratio, in a range of 430 to 500 nm, as listed in Table 3.When the average light transmittance at the perpendicular position wasadjusted to the same level as Examples 7 and 8, the single plate averagelight transmittance was lower by about 1% and the contrast ratio wasalso inferior. Further, when the single plate average lighttransmittance was adjusted to the same level as Examples 7 and 8, theperformance of contrast ratio was greatly inferior, being ⅓ or less.

TABLE 3 Average light Single plate transmittance at average lightperpendicular Contrast transmittance position ratio Example 7 41.71%0.01% 3854 Example 8 41.68% 0.01% 3577 Comparative Example 3 40.89%0.01% 3041 (when average light transmittance at the perpendicularposition was adjusted) Comparative Example 3 41.67% 0.04% 1037 (whensingle plate average light transmittance was adjusted)

INDUSTRIAL APPLICABILITY

The azo compound and a salt thereof of the present invention are usefulas dyes for polarizing films. Accordingly, the compound and the salt areused for various liquid crystal display devices and liquid crystalprojectors. More specifically, they are suitable for in-vehicleapplications and display applications for industrial instruments.

1. An azo compound represented by the following formula (1) and a saltthereof:

wherein R1 and R2 each independently represent a hydrogen atom, and n is1.